Generally, the existing clamping structure for a handled tool comprises a chuck body, grippers, nuts, bearings, an anti-loose device and an outer sleeve. The chuck body is connected to the driving spindle of the power device. The three grippers are mounted in three equally arranged guiding holes of the chuck body respectively. The grippers, provided with threads, produces screw transmission with the nuts. Rotating the outer sleeve connected to the nut will drive the grippers move along the guiding holes relatively to the chuck body resulting in the tool handle clamped or unclamped. The anti-loose device can prevent the handle from loosening off from the grippers when the tool is loaded and vibrated.
In above structure, because of the very large contact stress produced by the threads between the grippers and the nut under operating load, the relatively sliding friction is large, accordingly the clamping force for clamping the tool handle, produced by the screw transmission between the nut and grippers, is difficult to be large enough, which results in that the grippers are incapable of clamping tightly the tool handle under the operating condition of heavy load and vibration. In addition, for those published anti-loose structures, the anti-loose effects are not good enough because of the structure limitation. For instance, in PCT/CN02/00375, there is a hidden trouble of looseness in the structure under the operating condition of vibration and strike.